In a time-of-flight mass spectrometer (which is hereinafter abbreviated as “TOFMS”), which is a type of mass spectrometer, ions derived from components contained in a sample are individually given a specific amount of energy and injected into a flight space. After being made to fly a specific distance, the ions are detected, and the time of flight of each ion is measured. Since the flying speed of an ion within the flight space depends on the mass-to-charge ratio (m/z) of the ion, the mass-to-charge ratio of each ion can be determined from the measured time of flight. The mass-resolving power of the TOFMS normally increases with an increase in the distance which the ions are made to fly. However, if ions having the same mass-to-charge ratio are spatially spread in their direction of flight, it will be difficult for different kinds of ions having close mass-to-charge ratios to be separated from each other. Therefore, in order to improve the performance of the device, it is important to achieve both a longer time of flight by increasing the flight distance and the shortest possible period of time during which ions having the same mass-to-charge ratio are detected by the ion detector. This period of time is hereinafter called the “duration”.
In the case of a linear TOFMS, in which ions are made to fly linearly, or a reflectron TOFMS, in which ions are made to fly in a round-trip path by means of a reflecting electric field, increasing the flight distance requires the device to be larger in size. In recent years, a type of device called the “multiturn” TOFMS has been developed (for example, see Patent Literature 1, 2 or 4). In a multiturn TOFMS, ions are made to fly multiple times in a closed loop path (such as a substantially circular path, substantially elliptical path, “8”-shaped path) or quasi-loop path (such as a helical path; in the following descriptions, a quasi-loop path is also regarded as one form of the loop path). Such a multiturn system can provide a far longer flight distance within a comparatively small space than the linear or reflectron TOFMS.
The duration of the ions having the same mass-to-charge ratios at the ion detection point depends on various factors, such as the initial state of the ions at the time when the ions are accelerated and introduced into the time-of-flight mass separator, aberration of the ion optical system, and time-resolving power of the ion detection section. Improvements have been achieved in each of those elements. In particular, recently developed ion detectors can operate at extremely high speeds which correspond to response times of sub-nanoseconds. A type of ion detector commonly used for TOFMS is an ion detector employing a microchannel plate (MCP) which generates electrons upon receiving an ion and multiplies the generated electrons (for example, see Patent Literature 3 or Non-Patent Literature 1). As compared to secondary electron multipliers (SEMs), MCPs have a shorter multiplication pathway and are therefore faster in response. Their response time is roughly within a range from 0.4 nsec to 1.5 nsec depending on the individual devices.